1. Field of the Invention
The invention relates to a backlight module and an optical device thereof, and more particularly to a side incident type backlight module and an optical film set thereof.
2. Description of Related Art
FIG. 1A is an exploded view of a conventional backlight module, and FIG. 1B is an enlarged diagram of a part of the backlight module of FIG. 1A after being assembled. Referring to FIG. 1A and FIG. 1B, in a conventional display device, a uniform surface light source required by a display panel is provided by a backlight module. A conventional backlight module 100 includes a light guide plate 110, a light source component 120, a reflection sheet 130, a lower frame 140a, an upper frame 140b, and a plurality of optical films 150. The light guide plate 110 has a light incident surface 111 and a light-emitting surface 112. The light source component 120 is a light emitting diode bar. The light source component 120 includes a plurality of light emitting elements 122, and the light emitting elements 122 are light emitting diodes (LEDs). The reflection sheet 130 is disposed under the light guide plate 110. The optical films 150, e.g. a diffusion sheet, a prism sheet, and a brightness enhancement sheet, etc., are disposed above the light guide plate 110 and limited to be located between the light guide plate 110 and the upper frame 140b. 
A light beam emitted by the light source component 120 enters the light incident surface 111 of the light guide plate 110, and is transmitted to another side opposite to the light incident surface 111 of the light guide plate 110 via total reflection. During the transmission of the light beam, the total reflection of the light beam is destroyed by micro-structures on a bottom surface 114 of the light guide plate 110, and the light beam is emitted from the light-emitting surface 112 of the light guide plate 110. The light guide 110 is capable of converting the light beam emitted by the light source component 120 to a surface light source and guiding the light beam to be transmitted to the optical films 150.
However, since the light source component 120 is disposed at a side of the light incident surface 111 of the light guide plate 110, the brightness at a position is gradually decreased as the distance between the position and the light source component 120 is increased. In other words, the brightness at a position close to the light source component 120 is higher, and the brightness at a position far away from the light source component 120 is lower. The brightness at the position far away from the light source component 120 may be enhanced because a part of the light beam is refracted by the micro-structures of the light guide plate 110 during transmission. However, since the light emitting elements 122 of the light source component 120 are LEDs and LEDs are point light sources, the brightness at the position close to the light emitting elements 122 is higher than the brightness at other positions. Such that partial hot spots at a side close to the light source component 120 occur and then result in non-uniform brightness. Besides, since the optical films 150 includes the diffusion sheet, the prism sheet, and the brightness enhancement sheet, etc. capable of condensing light beam or enhancing the brightness at the positive viewing angle, the problem of the partial hot spots may be easily observed and then result in the non-uniform brightness of the surface light source.
In order to solve the above problem, techniques related to the above are disclosed in TW Patent Publication No. 200700797 and TW Patent No. I286644 and I254823.